Summer Solstice

Second quarter of 2008 is almost gone! How many items in your “to-do-list of 2008” were completed?

This reminder came from the Summer Solstice.

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Astronomy bugs are all over me, especially reminders of the time of the year. When I look at the calendar, I don’t feel much, but when I look at the night sky, I can have a shock.

“What? That’s Orion in the west? Oh no, another month is gone…”

“What’s that bright thing in the east? Jupiter? in Sagittarius? Oh no, it’s June now!”

“What? Venus in the evening sky now? Oh no, time really flies…”

So today, when I saw the sentence “Tomorrow is Summer Solstice”, you can bet I just went “oh no” again… What have I completed this year? How many items in my to-do-list are marked “DONE!”? What are my plans to “save” the rest of the year so that I’ll not regret that I’ve done nothing when winter solstice is here?

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So, what is this summer solstice that give me a shock?

Summer solstice (or June solstice) is the time when the position of the Sun is farthest north of the celestial equator. It happens in June, around the 21st.

In the northern hemisphere, it is widely recognised as the beginning of summer and the beginning of winter in the southern hemisphere. Here at the equator, we will not feel any different, except when you look at the position of the Sun, it will rise in the farthest north of east and set farthest north of west.

The reason why the motion of our Sun seems to move from south to north and back to south again during the course of a year is due to the 23.5-deg tilt of our planet’s rotational axis and our motion around the Sun.

The word solstice is derived from Latin word “solstitium”; “sol” meaning Sun, and “sistere” meaning stand still. When the Sun touches its farthest point north/south, it will “u-turn” back. It is during this changing of direction that the Sun seems to stand still momentarily; hence this point of time is called the solstice.